The present invention relates to a radio device and a cellular phone, and particularly to a radio device and a cellular phone with which it is possible to achieve a reduction in size and enhancement of antenna efficiency and gain.
In recent years, in cellular phones, for example, incorporation of an antenna in a casing has been practiced in view of the demand for attaining higher convenience and novel designs. When the antenna is incorporated in the casing, however, it becomes susceptible to interference by the hand, head portion and the like of the human body. As a result, the antenna may possibly be deteriorated conspicuously in gain as compared, for example, with a whip antenna having an element capable of being drawn out of the casing.
As a technology for solving this problem, there have been made some proposals (see, for example, Patent References 1, 2, and 3 set forth below). The technology described in Patent Reference 1 is to physically prevent the hand of the user from covering the incorporated antenna portion by, for example, reducing the thickness of the casing surrounding the antenna.
On the other hand, the technology described in Patent Reference 2 ensures that the radiation direction of an incorporated antenna composed of any of a monopole antenna, an inverted F-type antenna, and a microstrip antenna avoids the side of the surface of the portable apparatus seated on a desk, thereby to render the antenna less susceptible to influences of the hands and metallic bodies and to improve the gain of the antenna.
Further, the technology described in Patent Reference 3, in relation to an antenna composed of a radiating conductor and a ground conductor, is to dispose the ground conductor between the human head portion side and the radiating conductor, thereby reducing the radiation to the human head portion side and improving the gain of the antenna.                Patent Reference 1: Japanese Patent Laid-open No. 2002-51125 (p. 3; FIG. 1)        Patent Reference 2: Japanese Patent Laid-open No. 2002-237762 (pp. 2-3; FIG. 2)        Patent Reference 3: Japanese Patent Laid-open No. Hei 7-79110 (pp. 3-4; FIG. 1)        
According to the technology of Patent Reference 1, however, although a gain-improving effect is obtained, the reduction in size of the cellular phone and the design thereof may be damaged.
The technology of Patent Reference 2 is effective in improvement of electric characteristics. However, when a metallic body is placed in the vicinity of the antenna, the antenna characteristics may be deteriorated conspicuously, so that it is impossible to reduce the size of the area surrounding the antenna.
The technology of Patent Reference 3 is based on the assumption that the antenna portion is not covered by a hand, and the technology is an effective approach under the assumed condition. In practice, however, this approach restricts the way the terminal apparatus is held by the user's hand, which is inconvenient. Besides, when the antenna portion is covered with a hand, the radiating conductor is located between the hand and the ground conductor, possibly leading to a marked deterioration of gain.